1. Field of the Invention
This invention relates to an image forming apparatus using the electrophotographic process, and particularly to an image forming apparatus such as a copier, a printer or a facsimile apparatus.
2. Related Background Art
In recent years, the downsizing and higher function of image forming apparatuses such as electrophotographic apparatuses have been advanced, while on the other hand, requirements such as improved reliability, system evolution, maintenance freedom and tenderness to human beings and environments have heightened, and various propositions have been made in order to meet those requirements.
For example, Japanese Patent Application Laid-Open No. 53-74037 (corresponding U.S. Pat. No. 4,162,843) proposes an image forming apparatus carrying thereon a plurality of photosensitive members (photosensitive drums) which are image bearing members for the outputting of color images, and sequentially transferring toner images while conveying a recording material (recording medium) by belt-shaped conveying means.
Also, there have been proposed many image forming apparatuses of the so-called intermediate transfer type in which toner images formed on a plurality of photosensitive members are sequentially superimposed onto an intermediate transfer member to thereby effect transfer, and further the toner images on the intermediate transfer member are collectively transferred to a recording material.
On the other hand, recently, there have appeared image forming apparatuses of a type called "cleaning simultaneous with developing" or "cleanerless" which eliminates cleaning means as an exclusive instrument by making developing means serve also as cleaning means for removing any toner residual on the surface of a photosensitive member after the transfer of a toner image to a recording material, particularly for the downsizing of the entire apparatus, the ecological countermeasure by being waste tonerless, the longer life of the photosensitive member and the curtailment of the amount of consumed toner per page (for example, Japanese Patent Application Laid-Open No. 59-133573, Japanese Patent Application Laid-Open No. 62-203182, Japanese Patent Application Laid-Open No. 63-133179, Japanese Patent Application Laid-Open No. 64-20587, Japanese Patent Application Laid-Open No. 2-51168, Japanese Patent Application Laid-Open No. 2-302772, Japanese Patent Application Laid-Open No. 5-2287, Japanese Patent Application Laid-Open No. 5-2289, Japanese Patent Application Laid-Open No. 5-53482, Japanese Patent Application Laid-Open No. 5-61383, etc.).
Cleaning simultaneous with developing is to shift any untransferred toner from a transferring portion to a developing portion, and collect it by a fog removal potential difference Vback which is the potential difference between a DC voltage applied to the toner bearing member (the toner supplying member and developing member) of developing means and the surface potential of the photosensitive member during the development in the next step and subsequent steps by the toner bearing member.
Again in the image forming apparatus of the above-described intermediate transfer type, it is eagerly waited for to adopt the cleaning simultaneous with developing system with the downsizing of the entire apparatus, the ecological countermeasure by the waste tonerless system, the extended life of the photosensitive member and the containment of the amount of consumed toner per page taken into account.
However, when the image forming operation (the developing operation, the transferring operation, etc.) is interrupted by the bad conveyance of a recording material conveyed onto a recording material bearing member or a recording material in the course of an image being formed on the intermediate transfer member, and the operation of discharging the recording material stagnating in the apparatus out of the apparatus is being performed, the amount of toner already formed on the photosensitive member and residual on the photosensitive member without being transferred to the recording material borne and conveyed by the recording material bearing member or to the intermediate transfer member becomes greater than usual. In the case of an image forming apparatus of the multiplex transfer type using the cleaning simultaneous with developing system as shown in Japanese Patent Application Laid-Open No. 5-53482, and when the cleaning simultaneous with developing system is applied to the above-described image forming apparatus of the intermediate transfer type, developing means is a mechanism for collecting the residual toner on the photosensitive member, and the above-mentioned great amount of residual toner passes under a charger for charging the photosensitive member to form a latent image and therefore, the charging potential of that portion lowers and when image formation is done next, there has occurred the phenomenon (hereinafter referred to as the "ghost") that the toner image formed on that portion becomes light or dense. Also, a great amount of residual toner adheres to the charger and causes the charging capability of the charger to be reduced, and it has required much time to properly charge such a great amount of residual toner and collect all of it into the developing means, and as the result, it has required much time to enter the next image forming operation.
Also, it has happened that a toner image already transferred to the recording material on the recording material bearing member or the intermediate transfer member during the occurrence of jam is counter-transferred to a photosensitive member disposed downstream thereof when it passes while contacting with that photosensitive member, and because the color of the toner image counter-transferred onto the photosensitive member and the color of the toner image formed on the photosensitive member disposed downstream differ from each other, toners of different colors are mixed together in the developing means to thereby cause color mixing and in the image formation thereafter, the colors of the final image change.
In order to avoid this problem, it is possible to adopt a construction in which when an abnormal situation such as the abnormal conveyance of a recording material happens when an image is being formed on the recording material conveyed onto the recording material bearing member or on the intermediate transfer member and the image forming operation is interrupted, the recording material bearing member or the intermediate transfer member and the photosensitive member are spaced apart from each other in the return sequence after the abnormal state has been eliminated, but there arises the problem that the construction of the apparatus becomes complicated and the cost thereof increases and the apparatus itself becomes bulky.